Hi,
Not sure if this is a duplicate of a similar question on Stackoverflow, but the underlying ORM for Activiti is iBatis.
The Activiti system tables are not created as JPL Entities and as such are not able to be searched using Hibernate.
However, you could use the existing Activiti schema to model a Hibernate persistence layer and then overload the current persistence layer with a custom one. This is not a trivial operation since persistence code is quite spread out in the system.
However, one of the main changes in the Activiti 6 engine (still in beta) is a better abstraction of the persistence layer to make such customizations easier to implement.
More details on the persistence layer changes in version 6 can be found here: http://activiti.org/slides2015paris/activiti6.pdf
Hope this helps,
Greg
